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  #1  
Old 05-19-2014, 10:32 AM
davidmij davidmij is offline
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Default Gas tank functions

Can you guys tell me how the stock gas tank on my 59 bird is designed.

There were a bunch of different kinds of gas caps at Autozone back when I replaced my tank two years ago. The guy looked up which one I needed and had to order it.

When I remove my cap I get a pretty good hiss from the built up pressure. If I'm correct the cap should be letting air into the tank, but not out - via the venting built into the cap.

Does that sound correct?

The reason I ask is because I now have the performance 410 engine - when I ran it at the drag strip it was missing at times, like it was not getting enough fuel. The guys on the FEpower site have told me they would suspect the 5/16 inch fuel line should probably be upgraded to a 3/8 inch.

Any thoughts?

regards, Dave J
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  #2  
Old 05-19-2014, 10:45 AM
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jopizz jopizz is offline
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Squarebird gas tanks use a vented cap. With a vented cap you will still get pressure build up and a release when you take the cap off. That is normal. As far as getting enough fuel are you using an electric fuel pump or the mechanical pump. Going to a larger line may help but if you are fuel starved an electric pump might be a better option.

John
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  #3  
Old 05-19-2014, 01:10 PM
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DKheld DKheld is offline
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You are correct about vented caps only letting air in to displace the volume left by the fuel that is being used. Not certain - but don't see how the old vented caps could only let air in. I understand on the newer style with one way valves but don't believe one way valves were used on gas caps in the 60's.

I had/have the same problem. Using one of the Canadian made replacement tanks on mine and have a clear filter before the pump. If I open the 4 barrels often (which I do - ) and looked at the filter it would be empty or just starting to fill back up (by the time I stopped and got the hood open).

This weekend I ran it without the gas cap and the filter was full every time I checked it which leads me to believe that the original gas cap is not vented or at least doesn't have sufficient venting for the amount of fuel being used. (after I replaced the fuel pump of course - thinking it was the problem).

Stant recommends a 10640 to replace the original. Here is a long list of cross references on the stant site. Not sure they would have sufficient venting but going to try a 10640 on mine. Seems to be center vented. Hoping that will cure my problem.
http://ww2.stant.com/modules/partLoc...m.cfm?id=10640

Below is the cap that was on my car when I inherited it from my Dad - pretty sure it is original - but it is possible that in the 30 years previous to me getting the car the cap was lost and a replacement installed. Although you can't see it - the cap does have a small factory punched hole (which I guess is the vent ) in the rubber ring to the inside of where it seals to the tank rim but there are no holes in the center of the metal cap so don't see how it is supposed to work if that is the "vent". Sure doesn't seem to work on the new tank.

Eric

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  #4  
Old 05-19-2014, 02:32 PM
davidmij davidmij is offline
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I'm using a stock (mechanical) fuel pump for a 1967 390 4 barrel.

I'm pretty sure my vented cap is working fine, it always has pressure and both the tank and cap are fairly new.

One of the guys on the FEpower site told me to try using grey duct tape instead of a gas cap, and poke an 1/8" hole in the top portion of the tape. That would allow for plenty of air flow when the motor was sucking hard on the gas tank.

My problem is that the car doesn't always have the problem here at home, and I don't have any place near me to test it out full throttle on a 1/4 mile.

The fuel pump I have is rated at 40 gph, max psi 6.5, min psi 5.25. This has a 5/16 inch line. I can't imagine that if i was able to run the car at 5000rpm for a full hour that it would go through 40 gallons of gas. Of course I can't test that thought, but hey.

So here's what I think I'll do. I'm going to replace the fuel line with 3/8 inch line. (The current line is original and should probably be replaced anyway) I'll replace the fuel pump with the one for a 428, it has 3/8 inch fittings, and flows at 45 gph, and 6.5 max, 5.25 min psi. I'll also replace the in line fuel filter with a 3/8 inch filter.

The only problem is that I don't know what size the fitting is on the gas tank. I would guess that it has a thread size that fits the 5/16" line and the fitting for the 3/8" line would be too big.

It seems to me that the in-line filter would be the most restrictive point in all this, maybe if I just replace that?

Eric, is your fuel filter before of after the pump? Do you think it may be restricting your flow?

thx Dave J
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Old 05-19-2014, 05:39 PM
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I guess my running the car with no gas cap was about the same as the duct tape method - probably a little more risky.

Pretty sure my buddy's 70 Torino Cobra with the 429 Corba Jet only has 5/16 line - can't imagine it would use any less fuel than your car.

Not sure on the tank fitting but if the pick-up tube in the tank is only 5/16? Maybe the additional volume of fuel in the 3/8 line will help keep the fuel flowing good enough until the engine starts using less fuel.

Good point Dave - my filter and lines are 5/16 (before the pump) but I have no idea how much or if it restricts flow - I also left the filter that screws into the carb in place because it seals better that way. The clear one can be disassembled for cleaning (you can see it just above the oil filter) and the one on the carb is new. Lines are new. Pump is new. Carb rebuilt. Only thing left on mine is the cap.



Good luck on yours - let us know what you find

(you know if there are not any pics of the Tbird going down the track - then it didn't happen )

Eric
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  #6  
Old 05-19-2014, 10:27 PM
davidmij davidmij is offline
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Hah, pictures, yes, I need to do that. I'll post them and a couple of videos on Picasaweb to share fairly soon. Watching my car, from the non power wheel side, just kind of mosey down the track isn't very exciting. A 15.13 ET at a mile high - I was hoping for a bit more. I WILL be going back with a better tuned car and a posi-trac before the summer ends. Plus a more experienced driver. I've definitely got the dragstrip monkey on my back. If I can get it down to the low 14's I'll be happy. I figure that's about the same as a low 13 at sea level.

Something occurred to me Eric. If you can see the plastic fuel filter refilling then it must have some air in there too, correct? I wonder if maybe it's sucking air in somewhere. Maybe it has a leak on the in side of the filter? Just another thing to consider I guess.

I agree with what you said about the 429 CJ. I looked up a filter for the 7.0 motor (428) and it shows a 3/8 inch pump. My 390 and a 67 Mercury 410 use the 5/16. Anyway, I get the feeling I may one day go to a 445 stroker (years from now) so the 3/8 line will be needed eventually.

Dave J
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  #7  
Old 05-20-2014, 12:45 AM
Tbird1044 Tbird1044 is offline
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Having spent a lot of time working with pumps in an industrial application I found that the worst thing you can do to a pump is restrict the suction side of the pump. Considering there is probably a strainer screen inside the tank and possibly a filter in the fuel pump, if anyone is adding another filter in the suction side of the pump, you could be starving the pump of liquid. It will definitely push more liquid on the pressure side than it will pull on the suction side. Now consider there is also a filter on the pressure side at the carburetor. If your being fuel starved, get rid of redundant filters and let the fuel flow. Also, the fitting on the gas tank is definitely for a 5/16" tubing flared fitting, which would probably mean that the line inside the tank is also 5/16". By replacing the external lines to 3/8", you will be reducing friction line loss overall, but will still have the smaller line restriction inside of the tank. Just food for thought.
Nyles
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  #8  
Old 05-20-2014, 07:51 AM
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Dakota Boy Dakota Boy is offline
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I had a sump welded onto the bottom of my new tank before I installed it. Then I ran 3/8" lines all the way to the carb.

Most likely overkill, but someday when I hit the lottery, I'll be all ready for a thirstier engine to go into the car.

the link below shows what I am talking about:
http://www.squarebirds.org/vbulletin...1&d=1300412538
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  #9  
Old 05-20-2014, 01:19 PM
davidmij davidmij is offline
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Yeah, I thought those small filters that screw into the carb were high flow filters. Maybe try removing the clear one and see if that fixes your problem - it's a quick, easy check Eric.

As for mine I'm afraid what Nyles says is very true. One of the guys on the FEpower site told me I may have to take the tank out and have a 3/8 set up welded in. I think I'll try the 3/8 line, a high flow filter, and a 3/8 45 gph pump - the pump is only $20. It that doesn't work, I'll try either an electric pump or a 3/8 sump tank.

Greg, can you tell me where you got that sump tank thing?

thx, Dave J
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  #10  
Old 05-20-2014, 02:55 PM
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I bought it from either Jegs or Summit. dont recall exactly.
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